The present invention generally relates to a method and an apparatus for predicting deterioration of a member constituting a part of a machine, apparatus, equipment or the like with the aid of a computer. More particularly, the present invention is concerned with a deterioration predicting method and apparatus which can profitably be used for prediction and/or detection of embrittlement, damage or injury of a member made of ferrite containing stainless steel and adapted to be operated or used in high temperature environments such as encountered in nuclear power plants, chemical plants or the like.
As a method of measuring embrittlement of a member or mechanical component (part) known heretofore in the art, there may be mentioned a method disclosed in JP-A-54-61981. According to this known method, embrittlement of stainless steel weld metals of austenite type is measured and the decision is made that embrittlement occurs when the content of .delta.-ferrite is decreased at least by 5% of the initial .delta.-ferrite content.
On the other hand, according to an inspection method for predicting the remnant use life of a member or part (mechanical component) exposed to a high temperature environment before it is ultimately destroyed, a specimen for test made of a same material as the member of concern of an existing machine, apparatus or equipment (hereinafter also referred to as the machine collectively) which is actually used or operated in a high temperature environment is hermetically disposed within a container in which a non-oxidizing atmosphere is maintained, wherein the electrical resistance of the specimen under test is measured in the state where the interior of the container is maintained at a substantially same temperature as that of the member of the existing machine to be inspected, to thereby predict the remnant use life of the member of concern by measuring the electrical resistance of the specimen under test. Reference may be made to JP-A-57-175947. To this end, a specimen of the same material as the member of the existing machine must be prepared separately.
Additionally, it is known to measure deterioration or degradation in the physical property of a low-alloy metal casting product such as a turbine casing which is brought about in the course of time lapse by disposing a specimen for test of the same material as the turbine casing within it. The specimen is taken out from the turbine casing after lapse of a predetermined period during which the specimen has been exposed to high temperature environment and then undergoes a test for determining the deterioration of the material forming the specimen. Reference may be made to JP-A-54-121192.
Besides, it is known to determine fatigue of a material by measuring the magnetic coercive force, as is disclosed in JP-A-48-28293. According to this known method, a specimen foil for test which is made of a material exhibiting the coercive force susceptible to variation with high sensitivity in dependence on the degree of fatigue of the material is affixed to a structural member of concern. Wherein variation in the coercive force of the specimen under test is measured through the medium of an electromagnet which is so designed and disposed as to generate magnetic force lines only in the surface of a portion of the member under inspection.
In the case of the last mentioned prior art method, no consideration is paid to differences existing between the member of the existing machine and the specimen tested such as, for example, differences in stress distribution, temperature distribution, internal texture and presence or absence of radioactive irradiation, thus giving rise to a problem in respect to the accuracy and reliability of the estimation of deterioration of the existing mechanical member due to the aging on the basis of the data obtained from the measurement of the separately provided test specimen.
It is further noted that the methods known heretofore are incapable of detecting accurately or precisely the state of embrittlement without the need for overall inspection of a member of concern and proved impractical for the inspection of the member as a whole when the member is difficult to access or when the area to be inspected is excessively large, as in the case of machines installed in nuclear power plants or chemical plants.